1. Field of the Invention
The present invention relates to new compounds that are a combination of covalently linked phthalocyanine and linear siloxane polymeric structures having a unique and novel combination of optical and rheological properties which are useful in protective eye wear, nonlinear optical devices and for optical data storage applications.
2. Description of the Related Art
Previously developed phthalocyanine materials have not possessed the handling and processing characteristics of a single-component fluid coupled with an optical transparency, nonlinear optical absorption and refraction, chemical stability and moisture resistance. These are desirable characteristics for use as thin films in nonlinear optical and optical recording applications. Known methods for preparing phthalocyanines as thin films include vacuum deposition (sublimation, molecular beam, laser desorption), spraying or casting of a fine suspension or solution, Langmuir-Blodgett transfer, mechanical abrasion, and dispersion in a binder. The transparent thin film is a highly desirable physical form for these materials as it allows utilization of the chromophore in optical applications such as optical limiting and optical recording media which typically involve as material response to irradiation with a laser.
The deposition method, optical quality, and stability of a phthalocyanine film are determined by the molecular structure and properties of the material. Without peripheral substituents, phthalocyanine compounds are microcrystalline and relatively insoluble. Thin film preparation by vacuum deposition or high pressure abrasive techniques must frequently be accompanied by high temperatures. The microcrystalline character and the presence of different crystalline polymorphs contribute to optical scattering. These effects diminish the transparency of the phthalocyanine film. Temperature variation and exposure to chemical vapors (including water) causes conversions between different crystalline forms further diminishing the quality of the film. (See M. S. Mindorff and D. E. Brodie, Can. J. Phys., 59, 249 (1981); F. Iwatsu, T. Kobayashi and N. Uyeda, J. Phys. Chem.,84, 3223 (1980); F. W. Karasek and J. C. Decius, J. Am. Chem. Soc.,74, 4716 (1952))
When peripheral substituents are bonded to the phthalocyanine, molecular packing efficiency and crystallinity are reduced, and the resultant materials may be soluble in a variety of solvents. Film forming techniques involving the use of solvents, such as simple evaporation methods and Langmuir-Blodgett transfer techniques, are feasible processing methods. However, many peripherally substituted phthalocyanines do not form films of good transparent optical quality. The peripheral groups need to be large in size and preferably of mixed isomer substitution to be effective. While crystalline packing is hindered by the presence of peripheral substituents, there are strong attractive van der Waal forces at work between the planar faces of phthalocyanine rings which result in the constituent molecules aggregating into ordered domains. These domains, if large enough, cause optical scattering which strongly deteriorates the transparency and optical quality of thin films. (See T. Kobayashi, in Crystals: Growth Properties and Applications, N. Karl, editor, Springer-Verlag, New York, Vol 13 (1991) pp. 1-63; A. Yamashita and T. Hayashi, Adv. Mater., 8, 791 (1996)).
The interaction between adjacent phthalocyanine rings in an aggregate also results in a strong electronic perturbation of the molecular structure and a broadening of its absorption in the visible spectrum. This interaction in many cases detracts from the sought after nonlinear optical properties. (See S. R. Flom, J. S. Shirk, J. R. Lindle, F. J. Bartoli, Z. H. Kafafi, R. G. S. Pong and A. W. Snow, in Materials Res. Soc. Proc., Vol. 247, (1992) pp 271-276).
Control of phthalocyanine aggregation is important first to reduce the ordered domain size below a threshold where optical scattering occurs and second to reduce the pertubation of the phthalocyanine electronic structure to a level where spectral broadening and excited state lifetime shortening do not seriously diminish the nonlinear optical absorption of the phthalocyanine chromophore. The former is critical since optical transparency is required for a device of the current invention to function. For sufficient control of optical scattering, the ordered molecular domain size must be smaller than the light wavelength of application interest (usually in the 350 to 1500 nm range). The latter is less critical, but significant improvement in nonlinear optical properties can be realized if aggregation can be reduced to dimer formation or less.
Aggregation can be totally eliminated by blocking the co-facial approach of phthalocyanine rings by axial substitution onto metal ions complexed in the phthalocyanine cavity. (See N. B. McKeown, J. Mater. Chem., 10, 1979 (2000); M. Brewis, G. J. Clarkson, V. Goddard, M. Helliwell, A. M. Holder and N. B. McKeown, Angew. Chem. Int. Ed., 37, 1092 (1998); A. R. Kane, J. F. Sullivan, D. H. Kenny and M. E. Kenney, Inorg. Chem., 9, 1445 (1970)). However, this approach is limited to a small number of tetravalent octahedrally coordinating metals such as silicon. For reasons discussed below, the nonlinear optical properties of this small group of metallophthalocyanines are not particularly useful. (See H. S. Nalwa and J. S. Shirk, in Phthalocyanines: Properties and Applications, C. C. Leznoff and A. B. P. Lever, editors, VCH Publishers, Inc., New York (1996) Ch. 3).
Another approach to aggregation control is to utilize very large peripheral substituent groups that hinder the co-facial approach of phthalocyanine rings. Classes of such peripheral substituents are flexible oligomers (see D. Guillon, P. Weber, A. Skoulios, C. Piechocki and J. Simon, Molec. Cryst. Liq. Cryst., 130, 223 (1985); P. G. Schouten, J. M. Warman, M. P. Dehaas, C. F. van Nostrum, G. H. Gelineck, R. J. M. Nolte, M. J. Copvyn, J. W. Zwikker, M. K. Engel, M. Hannack, Y. H. Chang and W. T. Ford, J. Am. Chem. Soc., 116, 6880 (1994)), dendrimers (see M. Kimura, K. Nakada, Y., Chem. Comm., 1997, 1215; M. Brewis, B. M. Hassan, H. Li, S. Makhseed, N. B. McKeown and N. Thompson, J. Porphyrins Phthalocyanines, 4, 460 (2000); M. Brewis, M. Helliwell, N. B. McKeown, S. Reynolds and A Shawcross, Tetrahedron Lett.,42, 813 (2000)), and capping groups (see D. D. Dominguez, A. W. Snow, J. S. Shirk and R. G. S. Pong, J. Porphyrins and Phthalocyanines, 5, 582 (2001)). Examples of these three types of peripheral groups have had limited success in reducing aggregation. In many cases where the large peripheral groups have significant structural symmetry and uniformity of size, liquid crystal formation with its consequent optical scattering has resulted. (See N. B. McKeown, Phthalocyanine Materials: Synthesis, Structure and Function, Cambridge University Press, Edinburgh (1998) pp. 62-86). The liquid crystallinity has been avoided by utilizing peripheral groups with irregular symmetry combined with hydrogen bonding functional groups (see R. D. George and A. W. Snow, Chem. Mater., 6, 1587 (1994)) or using a polydispersity of peripheral group chain lengths (see A. W. Snow, J. S. Shirk and R. G. S. Pong, J. Porphyrins Phthalocyanines, 4, 518 (2000)). In the former case an epoxy-amine chemistry was utilized and a non-birefringent organic glass was obtained, while in the latter case polyethylene oxide chemistry was employed and an isotropic liquid was obtained. The organic glass or liquid has very favorable melt processing characteristics.
Another requirement on the nature of the peripheral group is that it must be chemically inert toward the metal ions complexed in the phthalocyanine cavity. Many of the metal ions that instill very useful nonlinear optical properties to the phthalocyanine chromophore are moderately labile and may be removed from the phthalocyanine cavity by competing complexing agents. This is particularly true of the heavy metal ions. In previous work with phthalocyanine compounds having polyethylene oxide peripheral groups, it was found that the ethylene oxide structure was a strong enough competitor in complexing with a lead ion and remove it from the phthalocyanine cavity (E. M. Maya, A. W. Snow, J. S. Shirk, S. R. Flom, R. G. S. Pong and G. L. Roberts, xe2x80x9cSilicone Substituted Phthalocyanines for Optical Limiting Applicationsxe2x80x9d presented at 221st National American Chemical Society Meeting, San Diego, Calif., Apr. 5, 2001). To be useful for the current invention, the peripheral groups must not behave in this manner.
Regarding specific instances of tethering a siloxane group to a peripheral site of a phthalocyanine compound, only one example is known (U.S. Pat. No. 3,963,744). In this instance, the siloxane group is a tris(trimethylsiloxy)silylalkyl structure which is connected through an alkylsulfamide linkage to the phthalocyanine periphery. This material is claimed to be compatible with cross-linked silicone polymers for the purpose of acting as a dye or a pigment. This tris(trimethylsiloxy)silylalkyl structure is compact (highly branched with short-chains) and nonlinear. A compound with these characteristics does not form useful transparent thin films. Conversely, the present invention teaches linear polysiloxane structures. This linear quality is a critical feature in thin film processing and nonlinear optical property enhancement.
Finally, the nonlinear optical properties of phthalocyanine materials are strongly dependent on the identity of the species complexed within its cavity. While this species may range from two protons to a wide variety of transition and main group metal ions, phthalocyanines with complexed heavy metal ions such as tin, bismuth, mercury, indium, tellurium, and particularly lead display the strongest nonlinear optical properties (see U.S. Pat. No. 5,805,326; H. S. Nalwa and J. S. Shirk, in Phthalocyanines: Properties and Applications, Vol. 4, C. C. Leznoff and A. B. P. Lever, editors, VCH Publishers, Inc., New York (1996) Ch. 3). In the divalent state, these metal ions do not coordinate to axial ligands. Thus, such ligands cannot be utilized to block aggregation. Many of these metal ions are labile and can be easily displaced by competing chelating structures. This problem is particularly acute with the polyethylene oxide structure where the oxygen sites in this polymer chain coordinate with the metal ion resulting in its consequent removal from the phthalocyanine cavity and diminishment of nonlinear optical properties.
Accordingly, one objective of the present invention is to provide a modified phthalocyanine that forms a transparent film of high optical quality, free of scattering from solid or liquid crystalline domains.
Another objective of the present invention is to provide a phthalocyanine material that has been modified so that it is processable as an isotropic liquid or glass. Such processing includes: filling confined very small spaces (0.01 to 100 micron) by capillary action; mechanically producing a film by shearing between two flat surfaces; and casting a film by solvent evaporation.
A further objective of the present invention is to produce phthalocyanine films that display large nonlinear optical absorptions suitable for use in optical limiting applications.
A further objective of the present invention is to produce phthalocyanine films that have a large nonlinear thermal refraction to complement the nonlinear photochemistry in optical limiting applications.
A further objective of the present invention is to provide a phthalocyanine material that has been modified so that it is useful in the following applications: as a protective element in an optical limiting component of direct view optical goggles, periscopes, gun sights, and binoculars; as the active element in laser intensity control and passive laser intensity noise reduction devices; as an optical switching element in an optical communications circuit; and as a component in compact disks, DVD""s, optical cache memories, and holographic memories.
These and other objectives of the present invention are accomplished through covalent bonding of siloxane oligomer structures of appropriate number, chain length and size distribution to connecting sites at the periphery of the phthalocyanine ring structure and by complexation of appropriate heavy metal ions in the phthalocyanine cavity.